Mentholated cigarettes, particularly filtered varieties, have enjoyed increased popularity and now account for more than 20 percent of the total market in the United States, together with varying percentages of penetration in overseas markets. Most commonly, menthol is applied to tobacco as a concentrated menthol/ethanol spray and is volatilized when the cigarette is smoked. In some countries in which tobacco is taxed by weight, the menthol is applied to the paper making up the cigarette package and subsequently migrates to the tobacco during storage. Both these approaches, which place menthol on tobacco, have several inherent disadvantages. One is that, as the cigarette is smoked, about three-fourths of the menthol on the tobacco is lost to the "side stream" smoke and is unavailable for taste effect to the smoker. A second disadvantage is that during storage and distribution of cigarettes to ultimate retail outlets, varying amounts of menthol are lost from the tobacco through the package. Most cigarettes are between six weeks to four months old when they are finally smoked. undergoing different storage conditions depending on season and other factors, so that the resultant uniformity of mentholated cigarettes is much lower than would be desired.
Activated carbon is known to be a highly efficient cigarette filter material, particularly for gas phase components of the smoke which have been shown to be toxic. However, it has not found significant commercial use in mentholated cigarettes since, among other reasons, activated carbon adsorbs the greater part of the menthol before the menthol can be delivered from its original place on the tobacco to the smoker. In adsorbing the menthol, the carbon's ability to adsorb the undesirable components of the smoke is diminished.
The disclosure of Irby U.S. Pat. No. 3,236,244 is an example of the use of activated carbon as a carrier for menthol for its introduction to the smoke stream. This type of filter does not, even during smoking, deliver a large part of the menthol at all. The menthol tenaciously clings to the carbon, clogging the pores and rendering the filter very inefficient with respect to the smoke stream. Only about one-fifth of it is recovered to the smoker. Because the carbon is so heavily loaded with menthol, a substantial portion of the menthol is also lost during storage. And, the Irby filter releases comparatively more menthol on the first puffs than the last. Furthermore, the Irby invention is workable only with a large available outer surface area of activated carbon, and thus requires the use of a very fine granular activated carbon material that is nearly a powder. This fine granular carbon, which if used in significant quantity, is difficult to handle in manufacturing the filter, limits the filter designs which may be used, and may cause an undesirable pressure drop. A commercial embodiment of the Irby invention was available for about six years, but commercialization has since been abandoned.
In addition to menthol, other flavor ingredients for cigarettes have been included either as components of filters or as additives to the tobacco upstream of the filter. One such embodiment is disclosed in Eichwald et al. U.S. Pat. No. 3,144,024, which discloses the use of various flavoring agents, including sugars, in cigarettes using mainly cellulosic filters but also contemplating "charcoal" filters. It is not suggested by Eichwald et al. however, that any advantage may be obtained by a particular combination of the use of sugars and menthol, either in the filter or on activated carbon. The sugar, in other words, is contemplated as a flavoring agent in itself. The use of sugar in the present invention, as amplified below, is basically as a convenient, comparatively inexpensive, food grade material to modify the pore structure of activated carbon. This modifying agent is not released as a flavoring agent as in the method of Eichwald et al.